Much interest has been shown in essential fatty acids (EFAs) and particularly GLA in recent years, both in relation to prostaglandin (PG) metabolism and generally. The two common series of EFAs are the n-6 series, metabolites of linoleic acid, and the n-3 series, metabolites of alpha-linolenic acid. The structures and naming of the acids may for example be found in the applicants' published European patent specification No. A0132089 (84304610.3) along with a discussion of the role of GLA as a precursor of 1-series PGs and arachidonic acid as precursor of 2-series PGs. This discussion is brief but is given at length in earlier applications also referred to and reference may be made to European patent specification No. A0132089 and the earlier specifications for the whole background.